The water temperature hovered around freezing, putting emergency crews at risk of hypothermia.
The city of Sioux Falls is named after the Big Sioux River's cascading waterfalls in Falls Park, a tourist attraction where people often picnic or pose for wedding photos.
It's a popular spot in the summer and spring, drawing about 525,000 visitors annually, according the local visitors' bureau. For the first time in months, the temperature rose to around 50 degrees in Sioux Falls on Thursday.
The park was closed Friday as crews continued their recovery effort.
Fatal accidents are rare at Falls Park. In 2006, the body of 29-year-old Travis Hallan was found just north of the falls after his canoe tipped over. In 1999, 26-year-old Slavisa Andric drowned after losing his footing on rocks at the park. A bystander in 1997 pulled the body of 43-year-old Omar Iasi Ibrahim Warsame from the water below a bridge where he had been fishing.
Barthel said the city could perhaps prevent accidents by fencing off the entire area, but there's some inherent danger with a fast-moving river meandering through the city.
"The Falls is the crown jewel of our city," Barthel said. "I don't think we want to get to a position where we're going to be totally fencing it off."
The city rescheduled its annual lighting of The Falls green to mark St. Patrick's Day until Sunday because of the search effort.
Associated Press writer Kristi Eaton in Sioux Falls and Blake Nicholson in Bismarck, N.D., contributed to this report.
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